Fix concurrent changes on nscd aware files (BZ #23178)

As indicated by BZ#23178, concurrent access on some files read by nscd
may result non expected data send through service requisition.  This is
due 'sendfile' Linux implementation where for sockets with zero-copy
support, callers must ensure the transferred portions of the the file
reffered by input file descriptor remain unmodified until the reader
on the other end of socket has consumed the transferred data.

I could not find any explicit documentation stating this behaviour on
Linux kernel documentation.  However man-pages sendfile entry [1] states
in NOTES the aforementioned remark.  It was initially pushed on man-pages
with an explicit testcase [2] that shows changing the file used in
'sendfile' call prior the socket input data consumption results in
previous data being lost.

From commit message it stated on tested Linux version (3.15) only TCP
socket showed this issues, however on recent kernels (4.4) I noticed the
same behaviour for local sockets as well.

Since sendfile on HURD is a read/write operation and the underlying
issue on Linux, the straightforward fix is just remove sendfile use
altogether.  I am really skeptical it is hitting some hotstop (there
are indication over internet that sendfile is helpfull only for large
files, more than 10kb) here to justify that extra code complexity or
to pursuit other possible fix (through memory or file locks for
instance, which I am not sure it is doable).

Checked on x86_64-linux-gnu.

	[BZ #23178]
	* nscd/nscd-client.h (sendfileall): Remove prototype.
	* nscd/connections.c [HAVE_SENDFILE] (sendfileall): Remove function.
	(handle_request): Use writeall instead of sendfileall.
	* nscd/aicache.c (addhstaiX): Likewise.
	* nscd/grpcache.c (cache_addgr): Likewise.
	* nscd/hstcache.c (cache_addhst): Likewise.
	* nscd/initgrcache.c (addinitgroupsX): Likewise.
	* nscd/netgroupcache.c (addgetnetgrentX, addinnetgrX): Likewise.
	* nscd/pwdcache.c (cache_addpw): Likewise.
	* nscd/servicescache.c (cache_addserv): Likewise.
	* sysdeps/unix/sysv/linux/Makefile [$(subdir) == nscd]
	(sysdep-CFLAGS): Remove -DHAVE_SENDFILE.
	* sysdeps/unix/sysv/linux/kernel-features.h (__ASSUME_SENDFILE):
	Remove define.

[1] http://man7.org/linux/man-pages/man2/sendfile.2.html
[2] https://github.com/mkerrisk/man-pages/commit/7b6a3299776b5c1c4f169a591434a855d50c68b4#diff-efd6af3a70f0f07c578e85b51e83b3c3

12 files changed, 40 insertions, 310 deletions

diff --git a/ChangeLog b/ChangeLog
index 3d4f2373ff..adec735a6b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,21 @@
+2018-05-16  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
+
+	[BZ #23178]
+	* nscd/nscd-client.h (sendfileall): Remove prototype.
+	* nscd/connections.c [HAVE_SENDFILE] (sendfileall): Remove function.
+	(handle_request): Use writeall instead of sendfileall.
+	* nscd/aicache.c (addhstaiX): Likewise.
+	* nscd/grpcache.c (cache_addgr): Likewise.
+	* nscd/hstcache.c (cache_addhst): Likewise.
+	* nscd/initgrcache.c (addinitgroupsX): Likewise.
+	* nscd/netgroupcache.c (addgetnetgrentX, addinnetgrX): Likewise.
+	* nscd/pwdcache.c (cache_addpw): Likewise.
+	* nscd/servicescache.c (cache_addserv): Likewise.
+	* sysdeps/unix/sysv/linux/Makefile [$(subdir) == nscd]
+	(sysdep-CFLAGS): Remove -DHAVE_SENDFILE.
+	* sysdeps/unix/sysv/linux/kernel-features.h (__ASSUME_SENDFILE):
+	Remove define.
+
 2018-05-16  H.J. Lu  <hongjiu.lu@intel.com>
 
 	* sysdeps/x86_64/multiarch/strncat-c.c (STRNCAT_PRIMARY): Removed.
diff --git a/nscd/aicache.c b/nscd/aicache.c
index 6f7b038021..2095edf911 100644
--- a/nscd/aicache.c
+++ b/nscd/aicache.c
@@ -31,9 +31,6 @@
 
 #include "dbg_log.h"
 #include "nscd.h"
-#ifdef HAVE_SENDFILE
-# include <kernel-features.h>
-#endif
 
 
 typedef enum nss_status (*nss_gethostbyname4_r)
@@ -447,32 +444,7 @@ addhstaiX (struct database_dyn *db, int fd, request_header *req,
 	     would unnecessarily let the receiver wait.  */
 	  assert (fd != -1);
 
-#ifdef HAVE_SENDFILE
-	  if (__builtin_expect (db->mmap_used, 1) && !alloca_used)
-	    {
-	      assert (db->wr_fd != -1);
-	      assert ((char *) &dataset->resp > (char *) db->data);
-	      assert ((char *) dataset - (char *) db->head + total
-		      <= (sizeof (struct database_pers_head)
-			  + db->head->module * sizeof (ref_t)
-			  + db->head->data_size));
-# ifndef __ASSUME_SENDFILE
-	      ssize_t written;
-	      written =
-# endif
-		sendfileall (fd, db->wr_fd, (char *) &dataset->resp
-			     - (char *) db->head, dataset->head.recsize);
-# ifndef __ASSUME_SENDFILE
-	      if (written == -1 && errno == ENOSYS)
-		goto use_write;
-# endif
-	    }
-	  else
-# ifndef __ASSUME_SENDFILE
-	  use_write:
-# endif
-#endif
-	    writeall (fd, &dataset->resp, dataset->head.recsize);
+	  writeall (fd, &dataset->resp, dataset->head.recsize);
 	}
 
       goto out;
diff --git a/nscd/connections.c b/nscd/connections.c
index 5f91985859..1b3bae4eeb 100644
--- a/nscd/connections.c
+++ b/nscd/connections.c
@@ -46,9 +46,6 @@
 #include <sys/mman.h>
 #include <sys/param.h>
 #include <sys/poll.h>
-#ifdef HAVE_SENDFILE
-# include <sys/sendfile.h>
-#endif
 #include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/un.h>
@@ -285,26 +282,6 @@ writeall (int fd, const void *buf, size_t len)
 }
 
 
-#ifdef HAVE_SENDFILE
-ssize_t
-sendfileall (int tofd, int fromfd, off_t off, size_t len)
-{
-  ssize_t n = len;
-  ssize_t ret;
-
-  do
-    {
-      ret = TEMP_FAILURE_RETRY (sendfile (tofd, fromfd, &off, n));
-      if (ret <= 0)
-	break;
-      n -= ret;
-    }
-  while (n > 0);
-  return ret < 0 ? ret : len - n;
-}
-#endif
-
-
 enum usekey
   {
     use_not = 0,
@@ -1163,35 +1140,8 @@ request from '%s' [%ld] not handled due to missing permission"),
       if (cached != NULL)
 	{
 	  /* Hurray it's in the cache.  */
-	  ssize_t nwritten;
-
-#ifdef HAVE_SENDFILE
-	  if (__glibc_likely (db->mmap_used))
-	    {
-	      assert (db->wr_fd != -1);
-	      assert ((char *) cached->data > (char *) db->data);
-	      assert ((char *) cached->data - (char *) db->head
-		      + cached->recsize
-		      <= (sizeof (struct database_pers_head)
-			  + db->head->module * sizeof (ref_t)
-			  + db->head->data_size));
-	      nwritten = sendfileall (fd, db->wr_fd,
-				      (char *) cached->data
-				      - (char *) db->head, cached->recsize);
-# ifndef __ASSUME_SENDFILE
-	      if (nwritten == -1 && errno == ENOSYS)
-		goto use_write;
-# endif
-	    }
-	  else
-# ifndef __ASSUME_SENDFILE
-	  use_write:
-# endif
-#endif
-	    nwritten = writeall (fd, cached->data, cached->recsize);
-
-	  if (nwritten != cached->recsize
-	      && __builtin_expect (debug_level, 0) > 0)
+	  if (writeall (fd, cached->data, cached->recsize) != cached->recsize
+	      && __glibc_unlikely (debug_level > 0))
 	    {
 	      /* We have problems sending the result.  */
 	      char buf[256];
diff --git a/nscd/grpcache.c b/nscd/grpcache.c
index 0ed8e656b2..c01aeb1f1d 100644
--- a/nscd/grpcache.c
+++ b/nscd/grpcache.c
@@ -35,9 +35,6 @@
 
 #include "nscd.h"
 #include "dbg_log.h"
-#ifdef HAVE_SENDFILE
-# include <kernel-features.h>
-#endif
 
 /* This is the standard reply in case the service is disabled.  */
 static const gr_response_header disabled =
@@ -318,37 +315,9 @@ cache_addgr (struct database_dyn *db, int fd, request_header *req,
 	     unnecessarily let the receiver wait.  */
 	  assert (fd != -1);
 
-#ifdef HAVE_SENDFILE
-	  if (__builtin_expect (db->mmap_used, 1) && ! dataset_temporary)
-	    {
-	      assert (db->wr_fd != -1);
-	      assert ((char *) &dataset->resp > (char *) db->data);
-	      assert ((char *) dataset - (char *) db->head
-		      + total
-		      <= (sizeof (struct database_pers_head)
-			  + db->head->module * sizeof (ref_t)
-			  + db->head->data_size));
-	      ssize_t written = sendfileall (fd, db->wr_fd,
-					     (char *) &dataset->resp
-					     - (char *) db->head,
-					     dataset->head.recsize);
-	      if (written != dataset->head.recsize)
-		{
-# ifndef __ASSUME_SENDFILE
-		  if (written == -1 && errno == ENOSYS)
-		    goto use_write;
-# endif
-		  all_written = false;
-		}
-	    }
-	  else
-# ifndef __ASSUME_SENDFILE
-	  use_write:
-# endif
-#endif
-	    if (writeall (fd, &dataset->resp, dataset->head.recsize)
-		!= dataset->head.recsize)
-	      all_written = false;
+	  if (writeall (fd, &dataset->resp, dataset->head.recsize)
+	      != dataset->head.recsize)
+	    all_written = false;
 	}
 
       /* Add the record to the database.  But only if it has not been
diff --git a/nscd/hstcache.c b/nscd/hstcache.c
index 344a2b3052..6ef0c653ea 100644
--- a/nscd/hstcache.c
+++ b/nscd/hstcache.c
@@ -37,9 +37,6 @@
 
 #include "nscd.h"
 #include "dbg_log.h"
-#ifdef HAVE_SENDFILE
-# include <kernel-features.h>
-#endif
 
 
 /* This is the standard reply in case the service is disabled.  */
@@ -352,37 +349,9 @@ cache_addhst (struct database_dyn *db, int fd, request_header *req,
 	     unnecessarily keep the receiver waiting.  */
 	  assert (fd != -1);
 
-#ifdef HAVE_SENDFILE
-	  if (__builtin_expect (db->mmap_used, 1) && !alloca_used)
-	    {
-	      assert (db->wr_fd != -1);
-	      assert ((char *) &dataset->resp > (char *) db->data);
-	      assert ((char *) dataset - (char *) db->head
-		      + total
-		      <= (sizeof (struct database_pers_head)
-			  + db->head->module * sizeof (ref_t)
-			  + db->head->data_size));
-	      ssize_t written = sendfileall (fd, db->wr_fd,
-					     (char *) &dataset->resp
-					     - (char *) db->head,
-					     dataset->head.recsize);
-	      if (written != dataset->head.recsize)
-		{
-# ifndef __ASSUME_SENDFILE
-		  if (written == -1 && errno == ENOSYS)
-		    goto use_write;
-# endif
-		  all_written = false;
-		}
-	    }
-	  else
-# ifndef __ASSUME_SENDFILE
-	  use_write:
-# endif
-#endif
-	    if (writeall (fd, &dataset->resp, dataset->head.recsize)
-		!= dataset->head.recsize)
-	      all_written = false;
+	  if (writeall (fd, &dataset->resp, dataset->head.recsize)
+	      != dataset->head.recsize)
+	    all_written = false;
 	}
 
       /* Add the record to the database.  But only if it has not been
diff --git a/nscd/initgrcache.c b/nscd/initgrcache.c
index e21068fbf0..2c74951f57 100644
--- a/nscd/initgrcache.c
+++ b/nscd/initgrcache.c
@@ -29,9 +29,6 @@
 
 #include "dbg_log.h"
 #include "nscd.h"
-#ifdef HAVE_SENDFILE
-# include <kernel-features.h>
-#endif
 
 #include "../nss/nsswitch.h"
 
@@ -353,37 +350,9 @@ addinitgroupsX (struct database_dyn *db, int fd, request_header *req,
 	     unnecessarily let the receiver wait.  */
 	  assert (fd != -1);
 
-#ifdef HAVE_SENDFILE
-	  if (__builtin_expect (db->mmap_used, 1) && !alloca_used)
-	    {
-	      assert (db->wr_fd != -1);
-	      assert ((char *) &dataset->resp > (char *) db->data);
-	      assert ((char *) dataset - (char *) db->head
-		      + total
-		      <= (sizeof (struct database_pers_head)
-			  + db->head->module * sizeof (ref_t)
-			  + db->head->data_size));
-	      ssize_t written = sendfileall (fd, db->wr_fd,
-					     (char *) &dataset->resp
-					     - (char *) db->head,
-					     dataset->head.recsize);
-	      if (written != dataset->head.recsize)
-		{
-# ifndef __ASSUME_SENDFILE
-		  if (written == -1 && errno == ENOSYS)
-		    goto use_write;
-# endif
-		  all_written = false;
-		}
-	    }
-	  else
-# ifndef __ASSUME_SENDFILE
-	  use_write:
-# endif
-#endif
-	    if (writeall (fd, &dataset->resp, dataset->head.recsize)
-		!= dataset->head.recsize)
-	      all_written = false;
+	  if (writeall (fd, &dataset->resp, dataset->head.recsize)
+	      != dataset->head.recsize)
+	    all_written = false;
 	}
 
 
diff --git a/nscd/netgroupcache.c b/nscd/netgroupcache.c
index 2f187b208c..2b35389cc8 100644
--- a/nscd/netgroupcache.c
+++ b/nscd/netgroupcache.c
@@ -413,33 +413,7 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
 	 since while inserting this thread might block and so would
 	 unnecessarily let the receiver wait.  */
     writeout:
-#ifdef HAVE_SENDFILE
-      if (__builtin_expect (db->mmap_used, 1) && cacheable)
-	{
-	  assert (db->wr_fd != -1);
-	  assert ((char *) &dataset->resp > (char *) db->data);
-	  assert ((char *) dataset - (char *) db->head + total
-		  <= (sizeof (struct database_pers_head)
-		      + db->head->module * sizeof (ref_t)
-		      + db->head->data_size));
-# ifndef __ASSUME_SENDFILE
-	  ssize_t written =
-# endif
-	    sendfileall (fd, db->wr_fd, (char *) &dataset->resp
-			 - (char *) db->head, dataset->head.recsize);
-# ifndef __ASSUME_SENDFILE
-	  if (written == -1 && errno == ENOSYS)
-	    goto use_write;
-# endif
-	}
-      else
-#endif
-	{
-#if defined HAVE_SENDFILE && !defined __ASSUME_SENDFILE
-	use_write:
-#endif
-	  writeall (fd, &dataset->resp, dataset->head.recsize);
-	}
+      writeall (fd, &dataset->resp, dataset->head.recsize);
     }
 
   if (cacheable)
@@ -594,36 +568,9 @@ addinnetgrX (struct database_dyn *db, int fd, request_header *req,
       /* We write the dataset before inserting it to the database
 	 since while inserting this thread might block and so would
 	 unnecessarily let the receiver wait.  */
-       assert (fd != -1);
+      assert (fd != -1);
 
-#ifdef HAVE_SENDFILE
-      if (__builtin_expect (db->mmap_used, 1) && cacheable)
-	{
-	  assert (db->wr_fd != -1);
-	  assert ((char *) &dataset->resp > (char *) db->data);
-	  assert ((char *) dataset - (char *) db->head + sizeof (*dataset)
-		  <= (sizeof (struct database_pers_head)
-		      + db->head->module * sizeof (ref_t)
-		      + db->head->data_size));
-# ifndef __ASSUME_SENDFILE
-	  ssize_t written =
-# endif
-	    sendfileall (fd, db->wr_fd,
-			 (char *) &dataset->resp - (char *) db->head,
-			 sizeof (innetgroup_response_header));
-# ifndef __ASSUME_SENDFILE
-	  if (written == -1 && errno == ENOSYS)
-	    goto use_write;
-# endif
-	}
-      else
-#endif
-	{
-#if defined HAVE_SENDFILE && !defined __ASSUME_SENDFILE
-	use_write:
-#endif
-	  writeall (fd, &dataset->resp, sizeof (innetgroup_response_header));
-	}
+      writeall (fd, &dataset->resp, sizeof (innetgroup_response_header));
     }
 
   if (cacheable)
diff --git a/nscd/nscd-client.h b/nscd/nscd-client.h
index 831eb5acbf..624effabb4 100644
--- a/nscd/nscd-client.h
+++ b/nscd/nscd-client.h
@@ -446,8 +446,6 @@ extern ssize_t __readvall (int fd, const struct iovec *iov, int iovcnt)
   attribute_hidden;
 extern ssize_t writeall (int fd, const void *buf, size_t len)
   attribute_hidden;
-extern ssize_t sendfileall (int tofd, int fromfd, off_t off, size_t len)
-  attribute_hidden;
 
 /* Get netlink timestamp counter from mapped area or zero.  */
 extern uint32_t __nscd_get_nl_timestamp (void)
diff --git a/nscd/pwdcache.c b/nscd/pwdcache.c
index 4c3ab66021..997d7c08fc 100644
--- a/nscd/pwdcache.c
+++ b/nscd/pwdcache.c
@@ -35,9 +35,6 @@
 
 #include "nscd.h"
 #include "dbg_log.h"
-#ifdef HAVE_SENDFILE
-# include <kernel-features.h>
-#endif
 
 /* This is the standard reply in case the service is disabled.  */
 static const pw_response_header disabled =
@@ -296,37 +293,9 @@ cache_addpw (struct database_dyn *db, int fd, request_header *req,
 	     unnecessarily let the receiver wait.  */
 	  assert (fd != -1);
 
-#ifdef HAVE_SENDFILE
-	  if (__builtin_expect (db->mmap_used, 1) && !alloca_used)
-	    {
-	      assert (db->wr_fd != -1);
-	      assert ((char *) &dataset->resp > (char *) db->data);
-	      assert ((char *) dataset - (char *) db->head
-		      + total
-		      <= (sizeof (struct database_pers_head)
-			  + db->head->module * sizeof (ref_t)
-			  + db->head->data_size));
-	      ssize_t written = sendfileall (fd, db->wr_fd,
-					     (char *) &dataset->resp
-					     - (char *) db->head,
-					     dataset->head.recsize);
-	      if (written != dataset->head.recsize)
-		{
-# ifndef __ASSUME_SENDFILE
-		  if (written == -1 && errno == ENOSYS)
-		    goto use_write;
-# endif
-		  all_written = false;
-		}
-	    }
-	  else
-# ifndef __ASSUME_SENDFILE
-	  use_write:
-# endif
-#endif
-	    if (writeall (fd, &dataset->resp, dataset->head.recsize)
-		!= dataset->head.recsize)
-	      all_written = false;
+	  if (writeall (fd, &dataset->resp, dataset->head.recsize)
+	      != dataset->head.recsize)
+	    all_written = false;
 	}
 
 
diff --git a/nscd/servicescache.c b/nscd/servicescache.c
index 49d9d0dece..187207f7ea 100644
--- a/nscd/servicescache.c
+++ b/nscd/servicescache.c
@@ -278,37 +278,9 @@ cache_addserv (struct database_dyn *db, int fd, request_header *req,
 	     unnecessarily keep the receiver waiting.  */
 	  assert (fd != -1);
 
-#ifdef HAVE_SENDFILE
-	  if (__builtin_expect (db->mmap_used, 1) && !alloca_used)
-	    {
-	      assert (db->wr_fd != -1);
-	      assert ((char *) &dataset->resp > (char *) db->data);
-	      assert ((char *) dataset - (char *) db->head
-		      + total
-		      <= (sizeof (struct database_pers_head)
-			  + db->head->module * sizeof (ref_t)
-			  + db->head->data_size));
-	      ssize_t written = sendfileall (fd, db->wr_fd,
-					     (char *) &dataset->resp
-					     - (char *) db->head,
-					     dataset->head.recsize);
-	      if (written != dataset->head.recsize)
-		{
-# ifndef __ASSUME_SENDFILE
-		  if (written == -1 && errno == ENOSYS)
-		    goto use_write;
-# endif
-		  all_written = false;
-		}
-	    }
-	  else
-# ifndef __ASSUME_SENDFILE
-	  use_write:
-# endif
-#endif
-	    if (writeall (fd, &dataset->resp, dataset->head.recsize)
-		!= dataset->head.recsize)
-	      all_written = false;
+	  if (writeall (fd, &dataset->resp, dataset->head.recsize)
+	      != dataset->head.recsize)
+	    all_written = false;
 	}
 
       /* Add the record to the database.  But only if it has not been
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 8f19e0efc3..cd6244f7ea 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -190,7 +190,7 @@ CFLAGS-mq_receive.c += -fexceptions
 endif
 
 ifeq ($(subdir),nscd)
-sysdep-CFLAGS += -DHAVE_EPOLL -DHAVE_SENDFILE -DHAVE_INOTIFY -DHAVE_NETLINK
+sysdep-CFLAGS += -DHAVE_EPOLL -DHAVE_INOTIFY -DHAVE_NETLINK
 CFLAGS-gai.c += -DNEED_NETLINK
 endif
 
diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
index f65a262994..2ef2916a52 100644
--- a/sysdeps/unix/sysv/linux/kernel-features.h
+++ b/sysdeps/unix/sysv/linux/kernel-features.h
@@ -37,9 +37,6 @@
    introduced.  If somebody cares these values can afterwards be
    corrected.  */
 
-/* The sendfile syscall was introduced in 2.2.0.  */
-#define __ASSUME_SENDFILE		1
-
 /* Some architectures use the socketcall multiplexer for some or all
    socket-related operations instead of separate syscalls.
    __ASSUME_SOCKETCALL is defined for such architectures.  */